1. Field of the Invention
The present invention relates to filters consisting of distributed-constant elements such as filters printed in microstrip lines.
The invention is more particularly concerned with a method of adjustment and particularly frequency adjustment of a microstrip-line printed filter and also relates to the filter which is obtained by means of this method.
2. Description of the Prior Art
Filters of this type, one example of which is illustrated in FIG. 1, comprise a dielectric substrate on which metallizations have been formed by etching, for example. These metallizations can have different shapes.
The possibility of frequency adjustment of filters of this type is considered as an important requirement.
Frequency adjustment of these filters is already known and is performed in a number of different ways. A first method consists in varying the length of the microstrips, for example by cutting part of these microstrips with a scalpel. This mode of adjustment of a filter is subject to the major disadvantage of being irreversible. This is particularly serious in the event that the desired adjustment value has been overstepped. Furthermore, by cutting part of these microstrips with a scalpel, there is a potential danger of causing damage to the substrate on which they are deposited, which is liable to give rise to an immediate variation of its electrical characteristics and to chemical degradation in the long term. Another mode of frequency adjustment of microstrip-line printed filters as illustrated in FIG. 1 consists in soldering capacitors to the ends of the strips. The method in accordance with the present invention permits filter adjustment and does not give rise to the disadvantages mentioned in the foregoing.